Various forms of workpiece holders have been in use for holding hollow workpieces for press fitting. For example, permanent magnets or electromagnets within a press tool have been used to hold metallic workpieces. However, the use of magnets inherently attracts metal chips, metal shavings and other fine metal particles to the press tool. This affects the press tool's ability to properly and accurately locate and press a workpiece. Some workpieces, such as valve seats, cup plugs and the like require a high degree of accuracy when pressed into a bore of a body to ensure that the workpieces are accurately located and firmly positioned within the body.
Other types of workpiece holders include spring loaded fingers built into the nose of a press tool. The main drawback to this type of workpiece holder is that it limits the size of the workpiece to be held because space is needed for the spring fingers, springs, pivots and other various pieces of the assembly. Split collet type tools have also been used to hold a hollow workpiece being pressed. However, these tools are fragile because the inside diameter of the collet has to be thin enough to flex and yet be made of hardened steel for wear.
Another non-magnetic workpiece holder is disclosed in U.S. Pat. No. 5,539,968. The press tool of the '968 patent uses a split ring to engage the inside surface of the workpiece which when received on the tool has a generally flat face received and seated on a flat face of the press tool. By compressing or shifting the split ring, the workpiece may shift laterally relative to the press tool with its axis remaining substantially parallel to the axis of the press tool. This limited lateral shifting of the workpiece facilitates pressing the workpiece into a bore which has an axis parallel to but slightly offset from the axis of the press tool so that the press tool and bore do not have to be perfectly coaxially aligned with each other. However, the engagement of the flat face of the workpiece and flat face of the press tool does not permit the workpiece to become tilted or shifted angularly relative to the press tool and thereby requires the axis of the press tool to be parallel to the axis of the bore for proper insertion of the workpiece into the bore.